The invention relates to a process for producing mouldings, especially optical lenses and specifically contact lenses, to a device for carrying out the process and to mouldings produced by the process or by means of the device, especially optical lenses and specifically contact lenses, according to the preamble of the respectively-independent patent claim.
Contact lenses, which it is intended to produce economically in large numbers, are preferably produced by the so-called mould or full-mould process. In this process, the lenses are produced in their final shape between two mould halves (moulds), so that neither subsequent machining of the surfaces of the lenses nor machining of the rim is necessary. Mould processes are described, for example in PCT-patent application WO 87/04390 or in EP-A 0 367 513.
Contact lenses produced in this way are mouldings of very low mechanical stability having a water content of more than 60% by weight. After their production, the lenses are further inspected by measurement, are then packed and subjected to heat sterilization at 121xc2x0 C. in an autoclave.
In the case of these known mould processes, the geometry of the contact lens to be produced is defined by the mould cavity. The rim of the contact lens is likewise formed by the mould, which usually consists of two mould halves. The geometry of the rim is defined by the contour of the two mould halves in the region in which they touch each other.
In order to produce a contact lens, first of all a specific amount of the flowable starting material is introduced into the female mould half. The mould is then closed by putting the male form half into place. The starting material is usually dispensed somewhat to excess, so that when the mould is closed, the excess quantity is expelled into an overflow space that adjoins the mould cavity on the outside. The subsequent polymerization or crosslinking of the starting material is carried out by means of irradiation with UV light or by the action of heat or another non-thermal method. In the process, both the starting material in the mould cavity and the excess material in the overflow space are hardened. In order to obtain fault-free separation of the contact lens from the excess material, good sealing or expulsion of the excess material must be achieved in the zone in which the two mould halves touch. Only in this way is it possible for fault-free contact lens rims to be obtained.
The materials used for these moulds are preferably plastics, such as polypropylene. The moulds are produced by injection moulding and used only once. The reason for this is, inter alia, that the moulds are to a certain extent contaminated by the excess material, are damaged when the contact lens is separated or are irreversibly deformed in subareas during the sealing of the mould.
In the case of the injection-moulded forms, fluctuations in the dimensions as a result of fluctuations in the production process (temperatures, pressures, material properties) also have to be expected. Furthermore, it is also possible for shrinkage of the moulds after the injection moulding to occur. These dimensional changes in the mould may lead to fluctuations in the parameters of the contact lens to be produced (peak refractive index, diameter, basic curve, central thickness etc.), as a result of which the quality of the lens is diminished, and hence the yield is reduced. Moreover, in the event of insufficient sealing between the two mould halves, the excess material is not separated cleanly, so that so-called webs are formed on the rim of the contact lens. If it is more pronounced, this cosmetic fault at the rim of the lens can also lead to irritation when such a lens is worm, for which reason such lenses have to be sorted out by means of an inspection.
In particular because of the requirements on the quality of the rim of the contact lens, the moulds are also used only once, since a certain deformation of the moulds in their marginal region cannot be ruled out with certainty.
U.S. Pat. No. 5,508,317 describes a new contact lens material which represents an important improvement in the chemistry of polymerizable starting materials for the production of contact lenses. The patent discloses a water-soluble composition of a prepolymer, which is put into the mould cavity and subsequently crosslinked photochemically. Since the prepolymer carries a plurality of crosslinkable groups, the crosslinking is distinguished by high quality, so that a finished lens of optical quality can be produced within a few seconds, without subsequent extraction or reworking steps being necessary. The improved chemistry of the starting material presented in the patent means that contact lenses can be produced at considerably lower costs, so that this makes the production of disposable wearable lenses possible.
EP-A-0 637 490 describes a process by means of which a further improvement in the production process of contact lenses using the prepolymer described in U.S. Pat. No. 5,508,317 can be achieved. In this case, the material is put into a mould consisting of two halves, the two mould halves not touching each other but having a thin gap of annular design arranged between them. The gap is connected to the mould cavity, so that excess lens material can flow away into the gap. Instead of polypropylene moulds that can be used only once, it is possible for reusable quartz/glass moulds to be used, since, following the production of a lens, these moulds can be cleaned rapidly and effectively off the uncrosslinked prepolymer and other residues, using water, on account of the water-soluble basic chemistry, and can be dried with air. By this means, high precision lens shaping can in particular also be achieved. The crosslinking of the prepolymer is carried out by means of irradiation, especially with UV light, the irradiation of the mould cavity being limited by means of a chromium mask. Thus, only the material which is in the mould cavity is crosslinked, so that high reproducibility of the rim shaping of the lens can be achieved without a positive connection between the two mould halves made of polypropylene. The uncrosslinked, shadowed prepolymer solution can easily be washed away from the dimensionally stable, crosslinked lens by using water.
The invention tackles the problem of improving the production process for contact lenses further, so that the production costs for contact lenses can be reduced further, and the production capacities can be increased, and, at the same time, high reproducibility of the lens parameters is provided. In particular, the production time should be shortened and a higher degree of automation should be achieved. The number of moulds which have to be exchanged should be as low as possible.
By means of the single mould-half alignment of the female and of the male mould halves of the mould, in conjunction with a production process that is carried out cyclically, it is possible for a higher degree of automation to be achieved. Single mould-half alignment enables all the necessary centring and adjusting elements to be fitted directly to the mould, and thus the mould halves are easily accessible to an automatic handling system. This means that the entire production of a contact lens can be automated within a cyclic process, as a result of which the production costs can be reduced drastically and, at the same time, the productivity of a production plant can be increased. Furthermore, by eliminating manual process steps, high reproducibility of the contact lenses produced is ensured, so that fluctuations in the quality of the individual lenses are largely ruled out.
Moreover, single mould-half alignment enables automation of the mounting of mould halves, the changing of mould halves and the cleaning of mould halves.
In particular, the rapid changing of a mould within a cyclic production process is made possible by single mould-half alignment, since the outlay for the adjustment is dispensed with.
Furthermore, in the case of single mould-half alignment, the identification of individual mould halves is also possible, i.e. even in the case of combining a plurality of individual moulds to form a unit, xe2x80x9cchaoticxe2x80x9d production is possible, since the respective dioptric power can be registered via a mould-half identification, and hence the correct packaging of the lenses can be ensured. For instance, in the case of n-parallel individual moulds, n different dioptric powers can be produced at the same time. If a number m of dioptric powers is no longer needed, then it is necessary only for the female individual mould halves to be exchanged and replaced by others.
Furthermore, as a result of combining a plurality of individual moulds to form modularly constructed units consisting of m or n moulds, flexible adaptation to various production capacities is possible.